Polyhydroxyalkanoates (PHAs) are accumulated as microbial intracellular carbon and energy reserves. These polymers represent a class of compounds with physical-chemical characteristics similar to petroleum-derived plastics such as polypropylene, polyethylene and polystyrene, but are environmentally compatible and totally biodegradable to carbon dioxide and water (Anderson A J, Dawes E A. Occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates. Microbiol Rev. 1990; 54:450-72; Madison L L, Huisman G W. Metabolic engineering of poly(3-hydroxyalkanoates): from DNA to plastic. Microbiol Mol Biol Rev. 1999; 63:21-53; Sudesh K, Abe H, Doi Y. Synthesis, structure and properties of polyhydroxyalkanoates: biological polyesters. Prog Polym Sci. 2000; 25:1503-1555). A number of microorganisms, including Ralstonia eutropha, Alcaligenes latus and several species of Pseudomonas (Choi J I, Lee S Y. Process analysis and economic evaluation for poly(3-hydroxybutyrate) production by fermentation. Bioprocess Eng. 1997; 17:335-342; Ren Q, De Roo G, Van Beilen J B, Zinn M, Kessler B, Witholt B. Poly(3-hydroxy-alkanoate) polymerase synthesis and in vitro activity in recombinant Escherichia coli and Pseudomonas putida. Appl Microbiol Biotechnol. 2005; 69:286-292; Slater S, Houmiel K L, Tran M, Mitsky T A, Taylor N B, Padgette S R, Gruys K J. Multiple β-ketothiolases mediate poly(β-hydroxyalkanoate) copolymer synthesis in Ralstonia eutropha. J Bacteriol. 1998; 180:1979-1987; Tsuge T, Fukui T, Matsusaki H, Taguchi S, Kobayashi G, Ishizaki A, Doi Y. Molecular cloning of two (R)-specific enoyl-CoA hydratase genes from Pseudomonas aeruginosa and their use for polyhydroxyalkanoate synthesis. FEMS Microbiol Lett. 1999; 184:193-198), have been shown to produce various polyesters with different subunits (Steinbuchel A, Valentin H E. Diversity of bacterial polyhydroxyalkanoic acids. FEMS Microbiol Lett. 1995; 128:219-228). The homopolymer PHB and the copolymer poly-3-hydroxybutyrate-co-poly-3-hydroxyvalerate (PHB-co-PHV) are the most widely studied and have been produced commercially to manufacture some finished products, which are primarily used in medical applications such as tissue engineering (Martina M, Hutmacher D W. Biodegradable polymers applied in tissue engineering research: a review. Polym Int. 2007; 56:145-157). Burkholderia (formerly Pseudomonas) cepacia has been shown to efficiently synthesize short-chain-length (scl) PHAs, such as PHB, PHV, and PHB-co-PHV. By incorporating PHV with PHB to form the copolymer, lower crystallinity and better elongation can be obtained which have been shown to exhibit more desirable mechanical properties (Keenan T M, Tanenbaum S W, Stipanovic A J, Nakas J P. Production and characterization of poly-beta-hydroxyalkanoate copolymers from Burkholderia cepacia utilizing xylose and levulinic acid. Biotechnol Prog. 2004; 20:1697-1704).
Many carbon sources, including xylose, galactose, glucose, glycerol and levulinic acid, have been used to support growth and scl-PHA production by B. cepacia (Keenan T M, Tanenbaum S W, Stipanovic A J, Nakas J P. Production and characterization of poly-beta-hydroxyalkanoate copolymers from Burkholderia cepacia utilizing xylose and levulinic acid. Biotechnol Prog. 2004; 20:1697-1704; Vandamme P, Holmes, B, Vancanneyt M, Coenye, T, Hoste B, Coopman R, Revets H, Lauwers S, Gillis M, Kersters K, Govan J R. Occurrence of multiple genomovars of Burkholderia cepacia in cystic fibrosis patients and proposal of Burkholderia multivorans sp. nov. Int J Syst Bacteriol. 1997; 47:1188-1200). Although it is feasible for these carbon sources to be used to produce PHAs in the laboratory, high production costs hamper large-scale commercial production and the cost of fermentation feedstocks can account for up to 50% of the overall production cost (Choi J I, Lee S Y. Process analysis and economic evaluation for poly(3-hydroxybutyrate) production by fermentation. Bioprocess Eng. 1997; 17:335-342; Choi J, Lee S Y. Factors affecting the economics of polyhydroxyalkanoate production by bacterial fermentation. Appl Microbiol and Biotechnol. 1999; 51:13-21). Several process stream feedstocks, such as cheese whey permeate (Yellore V, Desai A. Production of poly-3-hydroxybutyrate from lactose and whey by Methylobacterium sp. ZP24. Lett Appl Microbiol. 1998; 26:391-39), wood hydrolysate (Keenan T M, Nakas J P, Tanenbaum S W. Polyhydroxyalkanoate copolymers from forest biomass. J Ind Microbiol Biotechnol. 2006; 33:616-626), sugarcane molasses and corn steep liquor (Gouda M K, Swellam A E, Omar S H. Production of PHB by a Bacillus megaterium strain using sugarcane molasses and corn steep liquor as sole carbon and nitrogen sources. Microbiol Res. 2001; 156:201-207), have been used to produce PHAs in an attempt to reduce production costs.
Glycerol (approximately 10% of the final weight of biodiesel) (Pachauri N, He B. Value-added utilization of crude glycerol from biodiesel production: a survey of current research activities. American Society of Agricultural and Biological Engineering Annual International Meeting, Portland, Oreg., 9-12 Jul., 2006) is the major byproduct of the biodiesel industry. As biodiesel production has increased dramatically from 500,000 gallons in 1999 to 450 million gallons in 2007 (National Biodiesel Board, 2008), crude glycerol generated from the transesterification of vegetable oil has also been produced in large quantities. Recent publications by Mothes et al. (Mothes G, Schnorpfeil C, Ackermann J U. Production of PHB from crude glycerol. Eng Life Sci. 2007; 7:475-479) and Cavalheiro et al. (Cavalheiro J M B T, Dealmeida M C M D, Grandfils C, Dafonseca M M R. Poly(3-hydroxybutyrate) production by Cupriavidus necator using waste glycerol. Process Biochem. 2009; 44:509-515) described direct fermentation of biodiesel-glycerol to PHB by Cupriavidus necator with polymer production approaching 50% of dry microbial biomass. In addition, Papanikolaou et al. (Papanikolaou S, Fakas S, Fick M, Chevalot I, Galiotou-Panayotou M, Komaitis M, Marc I, Aggelis G. Biotechnological valorization of raw glycerol discharged after bio-diesel (fatty acid methyl esters) manufacturing process: production of 1,3-propanediol, citric acid and single cell oil. Biomass Bioenergy 2007; 32:60-71) demonstrated the production of 1,3-propanediol, citric acid, and cellular lipids (single-cell oil) from biodiesel-glycerol using three separate microbial fermentations. Despite the commercial use of glycerol in the food, pharmaceutical, cosmetics and other industries (Pachauri N, He B. Value-added utilization of crude glycerol from biodiesel production: a survey of current research activities. American Society of Agricultural and Biological Engineering Annual International Meeting, Portland, Oreg., 9-12 Jul., 2006), it is expensive to refine crude glycerol to the purity needed for these applications.
Citation or identification of any reference in Section 2, or in any other section of this application, shall not be considered an admission that such reference is available as prior art to the present invention.